Electronic attack

Code: radarsim/physics/ecm.py, radarsim/simulation/engine.py.

Every jammer-equipped target uses its own technique from the scenario (ecm_type). The Jammers on switch turns all of them on or off, and Technique can force one technique on every jammer to compare them.

Noise jamming

For a self-screening jammer of ERP \(P_j G_j\) and bandwidth \(B_j\) against a radar of bandwidth \(B_r\) (Schleher 1999, §4.2):

\[ \frac{J}{S} = \frac{P_j G_j\, 4\pi R^2\, B_r}{P_t G_t \sigma\, B_j}\cdot\frac{L_s}{L_j}, \qquad B_r/B_j \le 1 . \]

The jammer's one-way path suffers half the propagation and system loss of the radar's two-way path. Jamming enters the SINR after the matched filter divided by the compression gain, like thermal noise (Detection). Spot and barrage jammers differ only in bandwidth. With frequency agility on, the jammer has to spread over 10 % of the carrier frequency.

The burn-through range, where \(S/J\) reaches the required SNR, is

\[ R_{bt} = \sqrt{\frac{P_t G_t \sigma\, B_j}{4\pi P_j G_j\, \mathrm{SNR}_{req}\, B_r}} . \]

The self-check validate_burn_through_range confirms that calculate_jsr gives exactly \(-\mathrm{SNR}_{req}\) at this range. The event log reports when a jammed target is first detected despite jamming (burn-through).

DRFM deception

A digital RF memory captures the radar pulse and plays it back, delayed (range gate pull-off, RGPO) or Doppler-shifted (velocity gate pull-off, VGPO), with a gain over the skin return. The jammer state machine (idle → capture → pull → reset) uses the dwell, pull rate and maximum pull from the scenario. The false return appears as a ghost target moving away from the real one along the line of sight; in the pulse-Doppler processor it is injected phase-coherently into the CPI.

Chaff and decoys

Chaff clouds and decoys are radar objects in their own right, released at a given time, optionally from a named aircraft's position. Chaff has a large, Swerling 2 cross-section (many independently moving dipoles) that blooms and then decays,

\[ \sigma(t) = \sigma_{max}\,(1 - e^{-t/\tau_b})\,e^{-t/\tau_d}, \]

and falls slowly. A decoy flies its own course with its own RCS. Both are detected and tracked exactly like aircraft, which is the point: the radar cannot tell them apart by detection alone.

Validity

• No jammer antenna pattern or sidelobe jamming geometry beyond the self-screening case; stand-off jammers are not modelled.
• Noise jamming is treated as white Gaussian noise in the receiver band.